Nondestructive characterisation of MOVPE-grown CdTe and ZnTe epilayers by picosecond and nanosecond "excite-probe" techniques

ZnS epilayers were grown by pyrolytic metalorganic vapour phase epitaxy using diethyldisulphide (Et2S2) as sulphur alkyl precursor in conjunction with dimethylzinc-triethylammine. It is demonstrated that Et2S2 lowers the temperatures of the process by about 150°C with respect to Et2S, leading to growth rates around 0.5 mu m/hr just above 400°C. Mass spectrometry measurements allowed to determine the Et2S2 relative bond strengths by looking at the fragmentation path of Et2S2+. It turned out that the S-S bond is stronger than the S-C bonds in the Et2S2 molecule, possibly leading to a destabilization of the latters, which finally results into lower pyrolysis temperatures for the alkyl. 10 K cathodoluminescence (CL) spectra of ZnS show both free-to-bound and intense self-activated bands peaked at 3.683 eV and 2.58 eV, respectively. These emissions are attributed to unintentional Na and halogen (most probably Cl) doping of ZnS epilayers. Monochromatic CL images of ZnS samples evidenced the interplay between point-defects induced radiative emissions and non-radiative recombination associated to the ZnS extended defects.